A missing police pistol is connected to a series of recent heists and murders. Its owner WONG died earlier while pursuing suspects in the mountains. All doubts point to his partner KO (Lam Ka Tung), who miraculously returned unharmed.
Hotshot CIB inspector KA-ON (Andy On) is in charge of the serial murder investigation. He knows the only chance he has in cracking the case is to ask his mentor/former boss BING (Lau Ching Wan) to come out from retirement.
Bing is recognized as a gifted criminal profiler until he went mad several years ago. At his superior's farewell party, Bing sliced off his right ear with a meal knife and offered it as a present. Bing lives in seclusion with his beloved wife MAY (Kelly Lin) ever since.